Seems like a collation conflict. What happens if you specify the collation of the table variable?

Ex:

Declare @v_Temp_School Table (School Varchar (250) SQL_Latin1_General_CP1_CI_AS, Currency Varchar (20) SQL_Latin1_General_CP1_CI_AS)

Insert Into @v_Temp_School (School )

--insert into #Temp_MDL (school,currency)

select ueb.evs_name from evs_unitExtensionbase ueb

except

select distinct school from #Temp_MDL --collate SQL_Latin1_General_CP1_CI_AS

Select * From @v_Temp_School

Insert Into #Temp_MDL ( School , Currency )

Select School , '$' From @v_Temp_School